Add user rating markdown doc

docs/user_rating.md

@@ -0,0 +1,41 @@
+# User rating
+
+## Overview
+
+All mostro messages are [Parameterized Replaceable Events](https://github.com/nostr-protocol/nips/blob/master/01.md#kinds) and use `30078` as event `kind`, a list of standard event kinds can be found [here](https://github.com/nostr-protocol/nips#event-kinds)
+
+## Communication between users and Mostro
+
+All messages from/to Mostro should be a Nostr event kind 4, the content of the event should be a JSON-serialized string (with no white space or line breaks) of the following structure:
+
+- `version`
+- `order_id` (optional)
+- `pubkey` (optional)
+- `action` (https://docs.rs/mostro-core/latest/mostro_core/enum.Action.html)
+- `content` (optional https://docs.rs/mostro-core/latest/mostro_core/enum.Content.html)
+
+After a successful trade Mostro send a nip04 event to both parties to let them know they can rate each other, here an example how the message look like:
+
+```json
+{
+  "version": "0",
+  "order_id": "7e44aa5d-855a-4b17-865e-8ca3834a91a3",
+  "pubkey": null,
+  "action": "RateUser",
+  "content": null
+}
+```
+
+After a Mostro client receive this message, the user can rate the other party, the rating is a number between 1 and 5, to rate the client must receive user's input and create a new nip04 event to send to Mostro with this content:
+
+```json
+{
+  "version": "0",
+  "order_id": "7e44aa5d-855a-4b17-865e-8ca3834a91a3",
+  "pubkey": null,
+  "action": "RateUser",
+  "content": {
+    "RatingUser": 5 // User input
+  }
+}
+```